The formation of fin field-effect transistors involves the formation of recesses, and then filling the recesses with a semiconductor material in order to form semiconductor fins. For example, recesses may be formed between shallow trench isolation regions, and silicon germanium is grown in the recesses. With the increasingly down-scaling of the integrated circuits, the aspect ratio of the recesses becomes increasingly higher. This causes the difficulty in filling the recesses. As a result, voids and seams may occur in the semiconductor material that is filled in the recesses.